Ecological effects of weather modification, Bangtail Ridge, Bridger Range, Montana : relationships of
pocket gophers (Thomomys talpoides) to time of snow melt
by Brent Marshall Haglund
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE in Zoology
Montana State University
© Copyright by Brent Marshall Haglund (1972)
Abstract:
Miorotus montanus, montane vole, and Thomomys talpoides, pocket gopher, populations and the
vegetation of their grassland habitat were studied among early and late snow melt sites on the Bangtail
Ridge, Bridger Range in southwestern Montana. Early and late melt sites were selected from aerial
photographs prior to the study done in the summers of 1970 and 1971. Methods used included live
trapping, mound and plug counts, and snap trapping.
Pocket gopher activity and abundance were positively correlated with melt time. No change was
detectable in the vole populations between site types. A floristic shift was noted between early and late
melt sites. Some plant species were nearly restricted to specific melt environments. Forb diversity was
greater at early melt sites. Seven grass and sedge and ten forb species were more common on early melt
areas. Five grass and sedge and 19 forb species were more common with late melt. Litter increased
with late melt.
The floristic shift was believed most related to the change in insolation and soil moisture regimes
between the melt types. Pocket gophers were thought to be least common on early melt sites because of
frozen soil conditions and perhaps shallower soil associated with early melt. Statement of Permission to Copy
In presenting this thesis in partial fulfillment of the
requirements for an advanced degree at Montana State University,
I agree that the Library shall make, it freely available for. inrspection„
I further agree that permission for extensive copying
of this thesis for scholarly purposes may be granted by my major
professor, or, in his absence, by the Director of Libraries,
It
is understood that any copying or publication of this thesis for
financial gain shall not be allowed without my written permission.
Signature
i/
Date
ECOLOGICAL EFFECTS OF WEATHER MODIFICATION, BANGTAIL'RIDGE,
'BRIDGER RANGE, MONTANA: RELATIONSHIPS OF POCKET GOPHERS
(THOMOMYS TALPOIDES) TO TIME OF SNOW MELT
by
BRENT MARSHALL HAGLUND
A thesis submitted to the Graduate Faculty in partial
fulfillment- of the requirements for the degree
of
MASTER OF SCIENCE
in
Zoology
Head, Maj or Department
Chairman, Examining Committee
MONTANA STATE UNIVERSITY
Bozeman, Montana
June, 1972
iii
ACKNOWLEDGMENT
The author wishes to extend his appreciation to those who
assisted him during the course of the investigation:
D r 0 Robert
E«.Moore directed the study, aided in the field work, and assisted
in the preparation of the manuscript; Dr0 Theodore W 0 Weaver supplied
a great amount of much-needed field assistance and questioning en­
couragement, and critically read the manuscript; and Dr0 Don C 0
Quimby critically read the manuscript.
The author's wife, Dayle,
gave her encouragement and aided in the field work.
The study was
financed by the National Science Foundation, GB 20960<,
iv
TABLE OF CONTENTS
Page
VITA
o
o
o
e
o
e
e
ii
ACKNOWLEDGMENT . „
iii
LIST OF TABLES' . .
v
ABSTRACT . . „ „ .
vi
DESCRIPTION
METHODS
o
.
.
.
I
. .
3
.
o
SELECTION . .
MAMMALS . . .
VEGETATION .
RESULTS . . . . .
4
A.
INTRODUCTION
7
9
VEGETATION .
POCKET GOPHER
TRAPPING . ■4
9
13
16
DISCUSSION . . .
18
LITERATURE CITED
24
V
LIST OF TABLES
Table
Page
1. . Physical description of sites . . . . . . . . . . . . . .
2.
5
Mean frequency in percentage of identifiable plant
species at 144 to 154 one square meter plots at four
sites, and mean number of species per plot at each site.
Only species with a total percentage greater than
2 are listed . . . . . . . . . . . . . . . . . . . . . .
10
3.
Modified point estimates of cover . . . . . . . . . . . .
14
4.
Pocket gopher survey = Mean number of mounds and plugs
per square. Early melt melted before May 22, 1970.
Late melt areas melted after May 22, 1970 . . . . . . . .
15
Trapping results from 1970 and 1971. Numbers of
different individuals captured. Number of trap nights
and captures of Miorotus montanus per 100 trap nights
also listed- . . . o . . . . . . . . . . . . . . . . . . .
17
5.
vi
ABSTRACT
Miorotus montanus^ montane vole, and Thomomys talpoides3
pocket gopher, populations and the vegetation of their grassland
habitat were studied among early and late snow melt sites on the
Bangtail Ridge, Bridger Range in southwestern Montana. Early and
late melt sites were selected from aerial photographs prior to the
study done in the summers of 1970 and 1971. Methods used included
live trapping, mound and plug counts, and snap trapping.
Pocket gopher activity and abundance were positively correlated
with melt time. No change was detectable in the vole populations
between site types. A floristic shift was noted between early and
late melt sites. Some plant species were nearly restricted to
specific melt environments. Forb diversity was greater at early
melt sites. Seven grass and sedge and ten forb species were more
common on early melt areas. Five grass and sedge and 19 forb
species were more common with late melt. Litter increased with
late melt.
The floristic shift was believed most related to the change
in insolation and soil moisture regimes between the melt types.
Pocket gophers were thought to be least common oh early melt sites
because of frozen soil conditions and perhaps shallower soil
associated with early melt.
INTRODUCTION
This research represents an attempt to ascertain the possible
biological implications of weather modification on the small mammals,
mainly pocket gophers
(Thomomys taZpoi-des)- and montane voles' (M-Lcrotus .
montanus)3 of a grassland-forest mosaic in southwestern Montana„
Within the grasslands, on early and late melt sites, the vole and
pocket gopher populations were measured for abundance and activity,
A vegetation study was done as a complement.
The study was carried out on the Bangtail Ridge of the Bridger
Range, Montana, during the summers of 1970 and 1971,
The ridge is the
target area for a Montana State University winter weather modification
project.
Other researchers have chosen this area as a study area
because of anticipated changes in winter precipitation on the ridge,
Both early melt and late melt areas are present on the ridge.
In some extreme cases the melting dates may be three months apart„ •
The assumption was made that the biota of these distinctive areas has
adapted to the different melting regimes in some, more or less, uniform
manner.
Therefore, if valid comparisons among the different melt sites
can be established it may be possible to predict the effect of a more
extensive snow pack.
The increase in late melt area would be due to
increased snowfall from cloud seeding operations.
In this case, a montane vole population low, differential grazing
pressure, mammal movement, plus normal biological variability have
—2—
combined to obscure some possible site differences among the small
mammal populations.
Pocket gopher numbers were shown to increase with
late melt and various plant species respond to changing melt dates by
becoming more or less common.
Perhaps a study carried out along the
environmental gradient of snow melt would have been more fruitful.
This research was supported by National Science Foundation Grant,.
GB 20960.
DESCRIPTION
The Bangtail Ridge extends along a NW-SE axis approximately 11
kilometers while reaching a peak elevation of 2434 meters, Approximate
center of the ridge'is the Bangtail Ranger Station which is 24 km
northeast of Bozeman, Montana and 11 km nearly due east of Bridger
Peak in the Bridger Range„
Two of the intensive study sites are with­
in 4 km to the northwest of the Ranger Station.
The remaining two are
within 3 km to the southeast.
Despite occasional conglomerate outcrops on the ridge, all sites
are underlain by the andesitic sandstone (graywacke) of the Paleocene
Fort Union Formation (Roberts 1964).
Soils of the Bangtail Ridge
meadows are dark brown loams in both A and B horizons with an average
pH of 5.5 in both horizons (Buchanan 1972).
Buchanan found the thick­
ness of the A horizon in the meadows to be no greater than 3.9 cm.
In some portions of Sites I, 2, and 4, rock fragments and subsoil are
surficial.
METHODS
SELECTION-
The study began with selection of sites from a series
of aerial photographs of the Bangtail Ridge,
One set of photographs
had been taken May 22, 1970, the other June I, 1970=
Those areas free
of snow May 22, were considered early melt areas = The areas with
snow cover on June I, were defined as late melt=
Selection consisted of choosing those areas for study which were
most nearly characteristic of one melt period=
But on all sites ex­
cept Site 3, there are small areas which melted at a different time
than the major portion of the site=
lected.
In 1970, Sites 2 and 3 were se­
Sites I and 4 were added in 1971, to allow study of two sets
of areas of the same grazing type.
MAMMALSthree means:
Mammal surveys on the four trapping areas were done by
live trapping, snap trapping, and a count of newly made
pocket gopher mounds and plugs =
Studies were made on grids with 15
meter intervals located in the four sites = At Site I this was a 12
x 12 grid ? at Site 4 the grid was 10 x 15=
Sites 2 and 3 had non-
rectangular grids placed in them from forest edge to forest edge=
This resulted in the use of 154 traps in Site 2 and 150 traps in Site
3.
The sites are more fully described in Table 1=
Live trapping periods were monthly per meadow from July through
September, 1970, and from June through September, 1971=
Live traps
were opened for three consecutive nights at the corners of the squares
-5-
Table Io
Physical description of sites..
Site
Melt
Type
I
Early
Sheep
2
Early
3
Late
4 ■ Late
Grazing
Type
Location
Aspect.
Slope
Altitude
SE3S, Seco 36,
Ro 7E, T. IN
SE
2 deg
2340 m
Cattle
NW%, Seco 8,
R. SE, To IS
NW
5 deg
2360 m
Sheep
NE3?, Seco 35,
Ro 7E, To IN
E -
8 deg
2250 m
Cattle
NE3S,- Seco 7,
Ro SE, To IS
E
12 deg
2340 m
—6—
formed by the trap stakes =
On the three following consecutive nights
the traps were moved diagonally into the centers of the squares.
Due
to grazing interruption or snowfall,, some trapping nights within, a
period were not consecutive.
The longest interruption was three days.
Snap trapping, was done at Site I in July, 1970, by two investigators
of the International Biological Program.
They placed two snap traps
at each stake for five nights; the following five nights traps were
placed in the centers of the squares.
ously (Hoffman
Snap traps were open continu­
et dl* 1971)„
The montane voles and other small mammals that were live-trapped
were toe-clipped for identification; visually aged as adult, sub­
adult, or juvenile; sexed; and released.
Because of occasionally
inclement weather and transportation difficulties which delayed some
trap examinations, trap mortality was as high as 35% on cold, wet
nights.
Live-trapping was done with Sherman live traps baited with rolled
oats.
In cold weather cotton was added for warmth.
In 1970, traps
were usually checked for captures in the morning, closed during mid­
day, and reopened in the evening.
During 1971, traps were checked
only in the morning and remained open throughout the day.
The pocket gopher mound and plug survey was described in the
U. S . IBP Grassland Biome Methods Manual (1970).
obliterated by kicking.
All old mounds were
Forty-eight hours later the new mounds were
—7—
counted within each grid square«
This treatment was made in early
August, 1971, at all sites.
VEGETATION-
The vegetation of the four sites was compared for
plant frequency within one square meter circular plots centered at the
grid corners.
The plot was circumscribed by.a „56 m string (radius)„
In this manner, 144 to 154 plots per site were examined, and their
plant species listed.
These frequency measurements were made in a
period from 15 July through 10 August, 1971.
Plant cover was estimated by a modified point method at each stake
at the four site's.
A 15 dm cord was divided into decimeter intervals
by a dark, 0.25 cm mark.
At each mark I determined the type of vege­
tation directly below the mark or that which obscured the mark.
categories denoted were:
The
bare ground, litter, sedge, forb, and grass.
The cord was stretched out four times perpendicular to the axes of the
trap grid at a height of 2 cm.
stake in the sites.
Thus 60 "points" were observed at each
This analysis was made in the period from August
5 to 22, 1971, before either the cattle or sheep began grazing in a
particular site.
This point method will not yield absolute figures for plant cover;
instead these cover data should be interpreted as comparisons among
the four sites studied.
Goodall (1952) found that when larger "points"
comparable in size to those of this study, were used plant cover values
increased and bare ground decreased relative to estimates made with
—8—
small, nearly infinitesimal "points'.".
RESULTS
VEGETATION-
Plant frequency analysis is a measure of the
ubiquity of a species„
Data of mean number of grass and sedge and
forb species per plot are derived from the frequency figures„
These
and plant frequencies are itemized in Table 2„
Four grass and sedge species, with highest total frequencies,
were considered characteristic of the sites.
They are:
Festuoa
ILdahoensts3 Carex Lrevior3 Stipa sp„, and Danthonia intermedia.
ten forbs considered characteristic are:
The
Achillea millefOlium3 Myosotis
Sylvatioa3 Arenaria Oongesta3,Agoseris spp., Polygonum Listortoides3
Campanula rotundifolia3 Dodeoatheon Qongugens3 Lupinus Serigeus3-■
Cerastium arvensis3 and Delphinium Lioolor,
A number of plant species change frequency with melt variation,
and some apparently respond differently to grazing.
fied in Table 2.
For instance,
They are identi­
Carex filifolia was more common on each
of the early melt sites than it was on the late melt sites? therefore,
it was considered to be a late melt decreaser.
My data indicate that
five grass and sedge species and 19 forbs decrease with later melt.
Seven grass and sedge species and ten forb species increase with late
melt.
These changes are similar to those recorded by Weaver, 1972,
from 150 sites on the Bangtail.
Data recorded in Table 2 also reveal
reduced forb diversity on late melt areas but little change in average
grass and sedge diversity.
-10-
Table 2.
Mean frequency in percentage of identifiable plant species
at 144 to 154 one square meter plots at four sites, and mean
number of species per plot at each site. Only species with
a total percentage greater than 2 are listed.
Plant species
Site I
early.
sheep
n=144
Frequency (%/lm2)
Site 2
Site 3
early.
late,
cattle
sheep
n=154
n=150
Site 4late.
cattle
n=150
Z (%)
n=598
GRASSES AND SEDGES
Late melt decreasers
Cavex
VanthonyIa -LntevmedyIa
Festuoa idahoensis1
Koelevia ovistata
Luzula spioata
22
96
92
58
74
41
93
96
46
15
8
0
73
8
3
12
23
82
18
5
83
212
343
130
97
I
0
0
0
I
24
I
20
3
5
3
11
39
5
81
8
9
89
55
83
25
78
23
21
18
46
85
46
180
34
35
HO
113
231
77
44
76
0
58
3
73
70
I
13
32
30
47
68
12
6
45
68
I
12
62
192
261
70
95
103
6.05
6.31
14
3
23
2
Late melt increasers
Bvomus mavginata
Cavex geyevi1
Cavex podooavpa*
Melioa speotabilis
Phleum alpinum
Stipa sp.i
Tvisetum spioatum1
No melt trend
Agvopyvon sp.1
Cavex bveviov
Cavex oapitata
Poa oanbyi
Poa pvatensis1
Mean no. grass and
sedge spp./plot
5.47
.64
FORES
Late melt decreasers
Antennavia vosea^Avabis Uuttalli"2-
53
58
57
8
147
71
-11-
Table 2„
Conto
Plant species
Site I
early.
sheep
n=144
Frequency (%/lm2)
Site 2
Site 3
early.
late.
cattle
sheep
n=154
n=150
Site 4
late.
cattle
n=150
Z (%)
n=598
FORBS , cont.
Late melt decreasers, cont o
88
19
58
76
85
96
40
40
79
77
74
95
31
94
27
55
69
Arenavia oongesta
Avnioa- tonohoTphylta
Besseya oinevear
Campanula votundifolia1
Cevastium avvensis
Dodeoatheon oonjugens
Eviogonum fIavum1
Fvaseva speoiosa
Geum tviflovum
Lomatium oous
Lupinus sevioeus^Myosotis sylvatioa2
Phlox hoodii
Polygonum bisto.vtoides
Potentilla gvaoilis^
Saxifvaga vhomboidea
Zygadenus venosus2
318
29
160
266
223
251
98
63
200
107
239
338
68
267
'142
731
138
88
8
80
77
58
78
57
21
69
27
92
88
29
78
70
17
48
71
I
5
54
27
32
.0
I
3
0
36
78
I
44
12
0
17
71
I
17
59
53
45
I
I '
49
3
37
77
7
51
33
I,
4
19
6
I
I
2
16
2
3
4
2
79
38
71
44
9
78
3
18
28
51
75
17
2
58
11
77
70
5
11
60
216
65
75
103
24
176
75
26
43
113
85
74
91
80
89
71
357
294
Late melt increasers ■
43
Delphinium bioolov2
4
Epilobium minutum
Evythvonium gvandiflovum
I
Geranium visoossissium
0
2
Haokelia flovibunda
Micvostevis sp,3
5.
Potentilla ovina1
0
0
Rumex pauoifolius
0
Thelypodium sagittatum
0
Viola nuttallid
No melt trend
Aohillea millefolium2
Agosevis spp.
92
69
-12-
Table 2.
Cont.
Plant species
Site I
early,
sheep
n=144
Frequency (%/lm2)
Site 2
Site 3
early,
late,
sheep
cattle
n=154
n=150
Site 4
late,
cattle
n=15Q
Z (%)
n=598
FORBS, cont„
No melt trend, cont..
Ant&nnavia 'pulchervima
Artemisia miohauxiana
Clematis hirsutissima
Collinsia parviflora2
Delphinium ooeidentale
Draba sp„
Erigeron sp„1
Erysimum asperum
Fritillaria pudioa
Galium boreale
Gallardia aristata1
Mertensia oblongifolia1
Orthooarpus sp„
Oxytropis sp.1
Phaselia sp.
Polemonium sp.
Sedum spp.1
Seneoio sp.
Silene parryi
Taraxacum spp„1
Thlaspi alpestris
Townsendia montana
Mean no„ forb
spp„/plot*
3
0
0
8
0
0
2
0
0
0
0
3
4
I
0
0
0
59
6
30
21
I
16.43
57
0
9
3
0
I
37
3
0
63
13
10
0
29
■7
3
80
42
22
42
45
I
16.55
48
0
3
41
0
2
9
8
I
58
0
3
0
0
I
18
0
47
18
23
54
0
13.02
21
2
2 ■
3
3
0
24
0
I
38
11
6
0
3
0
5
5
51
5
92
14
13
13.48
IIncreases at cattle grazed sites
2Increases at sheep grazed sites
^Possibly misidentified, may be CoZlomi
La sp,
*Means tested by t-test and early melt means significantly
higher at P=O„05
129
2
14
55
3
3
72
11
2
159
24
22
4
33
8
26
85
199
51
187
134
15
-13-
Cover estimates made by a modified point method are summarized in
Table 3.
Forb cover (23-41%) predominated at three sites.
Grass cover
(23-36%) is next in importance, followed by bare ground (18-32%), litter
(2-7%), and sedge (2-15%)=
As mentioned in the methods section, the
percentage cover of bare ground is probably underestimated„
Analysis of these data by the t-test indicates that a greater
amount of litter is significantly correlated (P=OcOS) with late melt.
Bare ground increased significantly (P=O.05) on sheep grazed sites.
POCKET GOPHER-
Estimation of pocket gopher numbers was made by
a count of new mounds within all 225 m2 grid squares .■ These data are
listed in Table 4.
Though the four complete sites had significantly different numbers
of gophers, there is no correlation of numbers with either grazing
regime or melt date.
The Kruskal-Wallis rank sum test (Woolf 1968) with a
t-test of differences .(P=O.05) was used because one could not assume the
mounds were normally distributed.
Yet if each meadow is examined more closely> an increase of
pocket gopher mounds with late melt is apparent.
For instance, in
Site 2 the mean within those 40 squares which melted free after May
22, 1970, is 7.6.
Disregarding the early melt area in Site 4 raises
the average to 5.0 mounds per square in 94 squares.
The small area in
Site I (26 squares) which melted after May 22, 1970, has a mean count
of 4.0
-14-
Table 3»
Modified point estimates of cover.
Cover category
Site I
early,
sheep
n=8640
Cover (% of n points)
Site 2
Site 3
early,
late,
cattle
sheep
n=9120
n=9000
Site 4
late,
cattle
n=9000
2
4
7
6
Bare ground**
32
18
25
20
Porb
39
40
23
41
Grass
23
36
30
30
Sedge
4
2
15
3
Litter*
*Tested by t-test= Differences between late melt and early melt
sites significant at P=O.05.
**Tested by t-test. Differences between sheep grazed and cattle
grazed sites significant at P=0.05.
-15-
Table 4.
Pocket gopher survey. Mean number of mounds and plugs per
square. Early melt melted before May 22, 1970. Late melt
areas melted after May 22, 1970.
Site I
early,
sheep
Melt time
Site 2
early,
cattle
X
Site 3
late,
sheep
Site 4
late,
cattle
Total
X
X
X
Gophers/
hectare
-
1.6
2.6
14.1
53.1
Early
1.1
3.5
Late
4.0
7.6
11.7
5.0
9.8
Total
2.6
4.8
11.7
4.1
5.7
14.5
26.6
63.5
22.8
30.9
Gophers'/
hectare
—16—
The results from grouping of all early melt squares and all late
melt squares are also listed in Table 4,
The collective mean of early
melt squares is 2,6, and that of late melt squares is 9,8,
A t-test
analysis of the rank-sum averages indicates a significant level of
difference (P=O.05),
by assuming (Reid
The number of gophers per hectare was calculated
et al* 1966) that one gopher was present for each
8,2 mounds,
TRAPPING-
The trapping data in Table 5 provide evidence for a
major decline in the
Miovotus montanus population from 1970 to 1971,
Within the sites trapped both years, the 1971 total is less than a
tenth of that trapped in 1970,
There is no significant correlation of
M. montanus numbers with either melt date or grazing type.
with the
Correlated
M. montanus decline was a rise in the number of Pevomysous
manioutatus captured.
Species and numbers captured on the trapping sites were:
Clethvionomys gappevi3 red-backed vole (3); Eutamias amoenus3 yellow
pine chipmunk (3) ;
Miovotus montanus3 montane vole (153) ? Must'ela
fvenata3 long-tailed weasel (2)? Pevomysous manioulatus3 deer mouse
(36);
Sovex Oineveus3 masked shrew (2); Thomomys talpoides3 pocket
gopher (3); ■and ■Zapus
pvinoeps3 western jumping mouse (I),
-17-
Table 5.
Captured
species
Trapping results from 1970. and 1971. Numbers of different
individuals captured. Number of trap nights and captures
of Micvotus montanus per 100 trap nights also listed.
Site I
early,
sheep
Site 2
early,
cattle
Site 3
late,
sheep
Site 4
late,
cattle
Total
Mievotus montanus
1970
1971
43
3
88
5
' 12
0
h.t.
2
143
10
2
9
0
9
n.t.
12
2
34
2856
3648
2710
3500
n.t.
3500
8446
14104
n.t.
0 =06
1 =7
0.07
Pevomyseus manieulatus
1970
1971
0
4
Trap
nights
1970
1971
2880a
3456
Mievotus montanus captures
per 100 trap nights
n.t.
1.5
O
O
1970
1971
3.1
0.14
0.44
none
not trapped that year.
a U.S. IBP snap trapping. Done in July, 1970, with two snap
traps per stake for ten nights (Hoffman et al* 1971).
DISCUSSION
The most striking results in the vegetation analysis are large
changes in plant frequency among sites.
In the Bangtail Ridge grass­
lands fairly distinct late and early melt floras exist.
most restricted to late melt environments are:
Some species
Bromus marginata,
Phleum Olpvnum3 Melioa Speotahilis3 Geranium visoossissium3 Miorosteris ■
sp., and
Viola Huttallio
areas are:
Some species most restricted to early melt
Danthonia intermedia3 Koeleria Oristata3 Antennaria rosea3
Besseya Oinerea3 Eriogonum fIavum3 Lomatium oous3 Lupinus Serioeus3
Phlox hoodii3 and Zygadenus venosuso
The work of Weaver (1972) generally supports my findings■„
Billings and Bliss (1959) examined a snowbank environment, and they
discovered "marked floristic vegetational differences" along the
gradient of snow melt.
Cover measurements are significantly different only with regard
to,increased litter cover at late melt sites and increased bare ground
at sheep grazed sites compared to cattle grazed sites.
Perhaps the
increased litter values reflect increased plant production or lowered
decomposition rate with late melt.
The increase in bare ground with
sheep grazing substantiates my impression that on the Bangtail they
are very intensive grazers.
The factors, biotic and abiotic, which affect the Bangtail Ridge
grasslands are numerous =
But perhaps only a few differentially affect
-19-
ear Iy and late melt areas.
Many of- these phenomena may be easily
contrasted between melt types while others are difficult to measure
or observe.
A number of factors may cause a late melt site to be a less
rigorous environment for a plant than an early melt site.
Snow depth ■
is greater at late melt sites, and in winter this may be a protective
influence to the vegetations
the soil on areas with only a thin snow
cover may be more likely to freeze.
Snow depth and consequently late
melt reflect snow deposition from lowered wind speeds.
As Billings
and Bliss (1959). point out, lowered wind velocity on deeper snow
areas is maintained the year around; the effect of this in the summer
would be to reduce the possibility of soil deflation and the rate of
soil moisture evaporation.
Soil moisture is not clearly associated
with melt on the Bangtail grasslands (Buchanan 1972 and Weaver 1972).
Yet Billings and Bliss (1959) found that soil moisture became un­
available earlier under the early melting.portion of the snowbank,
thus limiting the growing season.
In other ways early melt sites may be less rigorous.
Early
melt areas offer a greater length of sun exposure to plants and
higher temperatures to facilitate growth.
Minerals may be less
easily leached out of early melt areas because of a lowered quantity
of water moving through the soil.
Soil qualities and exposure may
differ between the type of sites, but on the Bangtail these differences
-20-
have not been detected»
melt sites is likely.
Greater pocket gopher disturbance at late
But the net effect of gopher disturbance has
not been established, although certain plants such as dandelion
probably decline with more pocket gophers (Branson and Payne 1958,
Ellison and Aldous 1952, and Julander et aZ-. 1959) =
The floristic changes seen on the Bangtail grasslands result from
several factors.
Of these soil moisture and duration of sunlight
exposure probably have the greatest influence on species distribution.
Pocket gopher mounds and plugs are more abundant on late melt sites
than early melt sites on the Bangtail.
positive correlation of sign with
Reid
et al* (1966) recorded a
Thomomys tatpoides numbers. Using
their approximation of 8.2 mounds per gopher in 48 hours the late melt
areas carry about 14.1 gophers per ha.
The late melt density is nearly
equal to that found by Ward and Keith (1962) from Black Mesa, Colorado.
Hansen (1965) , also working at Black Mesa, found twicfe these densities.
Hoffman
et al* (1971) reported on combined trapping and mound count
from Site I in early July, 1970.
They determined 43.5 gophers per ha
to be present, many of which were immature.
This value is much greater
than the one I calculated for Site I (14.5/ha).
I feel that my figure
is more representative of the gopher standing crop since it was made
after most of the young gophers dispersed.
Gopher workings are more
abundant as young gophers attempt to establish territory (Reid
et al,
1966).
s~-
-21-
The positive correlation of
to the floristic shift.
Thomornys taZpoides may be a response
Some reports have indicated great declines
in pocket gopher numbers with 2,4-D induced floristic alterations
(Keith
et al, 1959, and Hull 1971).
But forb diversity decreases
with late melt on the Bangtail, and no correlation of forb production
with melt could be determined.
Also, on late melt sites more known
preferred gopher food plants become less common or show no change
with melt than became more common (Branson and Payne 1958, Tryon
1947, Ward and Keith 1962, and Aldous 1951).
Soil condition, though, related to freezing and moisture has been
cited as a factor controlling some aspects of pocket gopher activity
(Miller. 1948, Ingles 1949, and Ward 1960).
Ingles (1949) observed
winter pocket gopher movements into areas with unfrozen soil from
frozen areas.
It is my observation that many more winter casts of
pocket gophers reflecting more winter activity, are found on Bangtail
late melt areas than early melt areas (Tryon 1947).
Miller (1948)
positively correlated gopher mound building with moister soil.
There­
fore, I conclude that the poorer burrowing conditions on early melt
areas from soil freezing and perhaps lesser soil depth excludes many,
pocket gophers from becoming year-around residents.
This results in
a lowered pocket gopher population on early melt sites on the Bangtail
From the 1970 and 1971 data little may be said about the relation
of vole or mouse numbers 'as measured by trapping to snow melt .
Other
-22-
investigators (Hodgson 1970 and Findley 1951) correlated
Miovotus
montanus abundance with low soil moisture, only moderate amounts of
litter, and dry grassland or grass-forb communities =
negatively correlated
They both
M. montanus numbers with grass-sedge and mesic.
grassland sites.
An interesting phenomenon is the increase in deer mouse captures
with the vole decline.
Douglass (1970) also trapped many more deer
mice immediately following a montane vole crash.
He concluded that
the deer mice had been previously excluded from intensive use of some
areas by
M. montanus.
If the effect of winter weather modification were to enlarge the
Bangtail Ridge late melt area the plants and animals might respond.
The late melt flora would become more prevalent as would pocket gophers.
The relationship of pocket gophers and-their effect on range•quality
has not been well established, but generally their effect is negative
where the range had been greatly damaged by over grazing (Julander
et at. 1959 and Ellison and Aldous 1952) .
Ellison and Aldous (1952) actually noted slightly greater plant
production and more desirable soil qualities with more gophers.
Branson and Payne (1958) detected a decline in some undesirable range
plants, such as dandelion and yarrow, with gopher foraging but found
increased quantities of slender wheat grass.
As the Bangtail grass­
lands have not been seriously overgrazed, in my opinion, increased
-23—
gopher numbers will not seriously damage grazing qualities.
LITERATURE' CITED
1951„ The feeding habits, of pocket gophers (Thomomys
tdl'po'Ldes moovei,) in the high mountain ranges of central Utah,
Aldous,. C. Mo
Jo Maitim,- 32: 84-87 =
Billings, W. D. and L, C, Bliss. 1959. An alpine snowbank environment
and its effects on vegetation, plant development, and pro­
ductivity , Ecolo 40: 388-397.
Branson, F. A. and G. F. Payne. 1958. Effect of sheep and gophers
on meadows of the Bridger Mountains of Montana. J. Range Mgmt.
11: 165-169.
Buchanan, B. A. 1972. Ecological effects of weather modification,
Bridger Range area, Montana: Relationships of soil, vegetation,
and microclimate. Unpublished Ph.D. dissertation. Mont. State
Univ., Bozeman. 136 pp.
Douglass, R. J. 1970. A field study of interactions between montane
voles, Miorotus montanus nexus3 Hall and Hayward, and deer mice,
Peromysous manioulatus- sonoriensis3 Le Conte, in northern Utah.
Unpublished M.S. dissertation. Univ. of Utah, Salt Lake City.
44 p p .
Ellison, L.. and C. M. Aldous. 1952. Influence of pocket gophers on
vegetation of subalpine grasslands in central Utah. Ecol„ 33:
177-186.
Findley, J. S . 1951. Habitat preferences of four species of
in Jackson Hole, Wyoming. J. Mamm.. 32: 118-120.
Miorotus
GoodalI,- D . W. 1952. Some considerations in the use of point
quadrats for the analysis of vegetation. Austral. J. Sci. Res.,
B, 5: 1-41.
Hansen, R. M.
habitat.
1965. Pocket gopher density in an enclosure of native
J. Mamm. 46: 508-509.
Hodgson, J. R. 1970. Ecological distribution of Microtus montanus
(Peale) and Miorotus "pennsylvaniaus (Ord) in an area of geographic
sympatry in southwestern Montana. Unpublished Ph.D. dissertation.
Monti State Univ., Bozeman. 65 pp.
-25Hoffman, R. S.,.J. K„ Jones,,- Jr=, r and H. H= Genoways0 1971. Smallmammal survey on the Bison, Bridger, Cottonwood, Dickinson,- and
Osage sites. U. S. Inter. Biol. Prog. Tech. Rep. No.- 109.
Hull, Jr., A. C. 1971. Effects of spraying with 2,4-D upon abundance
of pocket gophers in Franklin Basin, Idaho. J. Range Mgmt.
24: 230-232.
Ingles, L.. G. 1949. Ground water and snow as factors affecting the
seasonal distribution of pocket gophers. J. Mamm. 30: 345-350.
Julander, 0., J. P. Low, and 0. W. Morris. 1959. Influence of pocket
gophers on seeded mountain range in Utah. J. Range Mgmt.
12: 219-224.
Keith, J. 0., R. M. Hansen, and A. L. Ward. 1959. Effect of 2,4-D
on abundance of-foods of pocket gophers. J. Wildl. Mgmt.
23: 139-145.
Miller, M. A.
1948.
Seasonal trends in burrowing of pocket gophers
(Thomomys), J. Mamm. 29: 38-44.
Reid, V. H., R. M. Hansen, and A. L . Ward. 1966. Counting mounds and
earth plugs to census mountain pocket gophers. J. Wildl. Mgmt0
30: 327-334.
Roberts, A. E . 1964. Geologic map of the Bozeman Pass Quadrangle,
Montana. G. Q. Map 1-399. U. S.- Geol. Survey, Dept, of the Int.
Tryon, Jr., C. A. 1947. The biology of the pocket gopher (Thomomys
talpoides) in Montana. Mont. State Coll., Bozeman. Ag. Expt.
Sta. Tech. Bull. No. 448. 30 pp.
U. S. Inter. Biol. Prog. 1970.
the Comprehensive Network.
Field Data Collection Procedures for
Tech. Rep. No. 35. 37 pp.
Ward, A. L. 1960. Mountain pocket gopher food habits in Colorado.
J. Wildl. Mgmt..24: 89-92.
Ward, A. L. and J. 0. Keith. 1962. Feeding habits of pocket gopherson mountain grasslands. Black Mesa, Colorado. Ecol. 43: 744-749.
Weaver, T. W. 1972. Ecological effects of weather modification:
Effect of melt date on mountain meadows. Preliminary draft.
—26Wool f, C o M. 1968. Principles of Biometry,
Inc, Princeton, N, J„ 268 pp„
D „ Van Nostrand Co,,
MONTANA STATE UNIVERSITY LIBRARIES
762 1001
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H123
cop. 2
Haglund, Brent M
Ecological effects
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